1. Field of the Invention
The present general inventive concept relates to an inkjet head, and more particularly, to a method of forming a piezoelectric actuator in a uniform shape, the piezoelectric actuator providing a driving force to eject ink from a piezoelectric inkjet head.
2. Description of the Related Art
Generally, inkjet heads are devices that can print a color image on a printing medium by ejecting droplets of ink onto a desired region of the printing medium. Depending on the ink ejecting method, the inkjet heads can be classified into two types: thermal inkjet heads and piezoelectric inkjet heads. The thermal inkjet head generates bubbles in the ink to be ejected by using heat and ejects the ink using expansion of the bubbles, and the piezoelectric inkjet head ejects ink using a pressure generated by deforming a piezoelectric material.
FIG. 1A is a sectional view illustrating a general structure of a conventional piezoelectric inkjet head, and FIG. 1B is a sectional view along a line A-A′ of FIG. 1A.
Referring to FIG. 1A and FIG. 1B, a manifold 11, a plurality of restrictors 12, and a plurality of pressure chambers 13 are disposed in a flow channel plate 10 to form an ink flow channel. A vibrating plate 20, which becomes deformed by driving a piezoelectric actuator 40, is bonded to an upper surface of the flow channel plate 10. A nozzle plate 30, having a plurality of nozzles 31, is bonded to a lower surface of the flow channel plate 10. The flow channel plate 10 and the vibrating plate 20 may be integrally formed, and so may the flow channel plate 10 and the nozzle plate 30.
The manifold 11 is a passage that supplies ink flowing from an ink storage (not illustrated) to each of the pressure chambers 13, and the restrictor 12 is a passage through which ink flows from the manifold 11 into each of the pressure chambers 13. The pressure chambers 13 are arranged along one side or both sides of the manifold 11 to store the ink to be ejected. The nozzles 31 are formed by penetrating the nozzle plate 30 and are each connected to a respective one of the pressure chambers 13. The vibrating plate 20 is bonded to an upper surface of the flow channel plate 10 to cover the pressure chambers 13. The vibrating plate 20 is deformed by the operation of the piezoelectric actuator 40 to supply the pressure variation, to eject ink, to each of the pressure chambers 13. The piezoelectric actuator 40 includes a lower electrode 41, a piezoelectric layer 42, and an upper electrode 43, which are successively stacked on the vibrating plate 20. The lower electrode 41 is formed on a whole surface of the vibrating plate 20 to serve as a common electrode. The piezoelectric layer 42 is formed on the lower electrode 41 so as to be located above each of the pressure chambers 13. The upper electrode 43 is formed on the piezoelectric layer 42 to serve as a driving electrode to apply a voltage to the piezoelectric layer 42.
The piezoelectric actuator 40 of the conventional piezoelectric inkjet head is, generally, formed as described below. The lower electrode 41 is formed by depositing a predetermined metal material at a predetermined thickness on the vibrating plate 20 using a sputtering process. The piezoelectric layer 42 is formed by coating a ceramic material of a paste state having a piezoelectricity at a predetermined thickness on the lower electrode 41 using a screen-printing process, and sintering the same. The upper electrode 43 is formed by coating a conductive material on the piezoelectric layer 42 using a screen-printing process, and sintering the same.
However, since the conventional piezoelectric layer 42 formed by the screen-printing tends to spread laterally because of a property of the material of the paste state, it is difficult to form the conventional piezoelectric layer 42 in a uniform thickness. That is, a middle portion of the piezoelectric layer 42 is thick, while both edge portions of the piezoelectric layer 42 are thin, as illustrated in FIG. 1B. The upper electrode 43, which is formed on the piezoelectric layer 42 by a screen-printing process, also may not be uniform in shape, area, and thickness, due to a fluidity of the paste. Particularly, since a thickness of the piezoelectric layer 42 is not uniform, a distance between the upper electrode 43 and the lower electrode 41, which are formed respectively on the upper surface and the lower surface of the piezoelectric layer 42, is not uniform. Accordingly, an electric field formed between the upper electrode 43 and the lower electrode 41 is also not uniform. In addition, when the upper electrode 43 is formed on the thin edge portion of the piezoelectric layer 42, an interval between the upper electrode 43 and the lower electrode 41 becomes a lot smaller, so that the upper electrode 43 and the lower electrode 41 may be shorted. Moreover, a paste may flow down along a curved surface of the piezoelectric layer 42 and directly contact the lower electrode 41 in the forming process of the upper electrode 43, leading to a defective piezoelectric actuator 40.
As described above, the conventional method of the piezoelectric actuator 40 cannot control formation of a uniform width, area, and thickness etc., of the upper electrode 43.